Peras



L. PERAS April 25, 1961 LOW-TENSION SPARK PLUGS FOR INTERNAL COMBUSTIONENGINES Filed April 1, 1958 LOW-TENSION SPARK PLUGS FOR INTERNALCOMBUSTION ENGINES Lucien Pras, Billancourt, France, assignor to RegieNationale des Usines Renault, Billancourt, France Filed Apr. 1, 1958,Ser. No. 725,618 Claims priority, application France Apr. 29, 1957 7Claims. (Cl. 313-131) The present invention relates in general to sparkplugs of mternal combustion engines and has specific reference to animproved low-tension spark plug.

It is already known to constitute the sparking element of spark plugsutilized for igniting the fuel mixture in internal combustion engines bythe discharge of a condenser in the form of a pair of electrodes spaced.004" to 0.012" apart, this gap being occupied by an insulating memberon which the ignition spark is caused to slip.

The assembly comprising the electrodes and insulator is usually calledcartridge.

Now it is the essential object of this invention to provide an improvedspark plug of this general character and more particularly theabove-defined cartridge which is characterized 'by a specificarrangement of the electrodes and insulator whereby the useful life andregulari-ty of the spark plugare increased to a substantial extent.

embodiment of a low-tension spark plug constructed in accordance withthe teachings of this invention.

In'the drawing, the electrodes of the spark plug are designated by thereference numerals 1 and 2. The electrode 1 consists of a disk ofrefractory metal such as tungsten or thoriated tungsten, and the otherelectrode 2 consists of a hollow cylinder also of refractory metal. Theelectrode'z is formed with an axial bore provided at one end with acavity or counterbore forming a shoulder 3 and adapted to receive aninsulating washer 4 constituting the spark supporting member seated onsaid shoulder. The diameter of this washer is very slightly smaller thanthat of the electrode 2. The interior of this electrode 2 is lined withinsulating material 5 such as boro'silicated glass up to the leveloccupied by the washer 4 bearing partly against this insulating liningand partly against the metal of the electrode 2. The insulator 5 may befitted by compressing glass in the electrode carried by a jig. Theelectrodes'l, 2 are not necessarily of straight cylindrical shape withan annular cross-section, as the cylinder section may be designed tosuit specific requirements of the combustion chamber. For the sake ofeconomy the electrodes may be made not entirely of solid refractorymetal but formed, for example, by welding a thin annulus of tungsten orthoriated tungsten on a steel body. The insulating washer 4 fits exactlyin its recess or counterbore and may be slightly greater than thisrecess as measured in the axial direction; in this case the electrode 1may have a greater diameter, or a diameter tube 10". ,the two electrodesby properly stacking at the upper end equal to or less than that .of theinsulating washer. If desired, its height may be equal to or smallerthanthat of the recess; in both cases the diameter of this electrode 1is smaller than that of the diameter of washer 4. The spark-supportinginsulator isnot necessarily a flat hollow cylinder as the chiefrequirement is that its shape accommodate that of the electrode;besides, it may also completely fill the grounded electrode 2 and form asubstitute for the insulator 5. The spark-supporting insulator 4 ispreferably made of refractory material having a reliable stability up to1000 C., that is, adapted to be heated to this temperature withoutmelting, decomposing or undergoing any physical deteriorationwhatsoever; thus, porcelain, sintered alumina, clay-bound alumina, and

the like constitute efficient materials for this purpose.

If desired, insulating materials of high dielectric capacity may be usedto-advantage. The interelectrode gap e is of the order of 0.012" to0.08" according to the type of insulating material utilized. The sparkplug body 6 consists of a metal member insulated by a porcelain filling8 and a Bakelite or like insulating cone 9 from the central steel tube10 in which extends the current lead-in rod. The rod 7 is axiallydisplaceable in The insulator is constantly pressed between of thecentral rod 7 a plurality of spring-steel dished washers 11. Thesewashers are disposed by pairs with their concavities facing each otherand they exert a certain pressure against a sealing gasket 12 forexample of .polytetrafiuoroethylene; this pressure is obtained by meansof an adequate nut 13 screwed on the rod 7.

Finally, the sparkingsurface may be enamelled with a suitablespark-supporting composition.

I claim: 1. In a low voltage spark plug having a tubular member, aspark-plug cartridge removably mounted in said body member comprising, atubular first electrode disposed concentric internally of said tubularbody member nular inner surface of said first tubular electrode defining50- said counterbore and having a substantially flat face coplanar witha substantially flat end of said electrode corresponding to saidelectrode end extending axially out of said body member, a discelectrode mounted coaxially with said tubular electrode and having atransverse dimension smaller than said insulator forming acircumferential gap of uniform dimensions between the disc electrode andthe tubular electrode thereby forming a sparking zone of uniformdimensions, and an electrically conductive, axially displaceable, memberdisposed extending axially in said tubular electrode and said bodymember and having a mushroom head for removably holding the discelectrode snug against said coplanarface surface of the insulator, meanscomprising a plurality of dished cooperatively disposed spring elementsdisposed externally of the tubular body member for adjustably applyingan axially directed tension to said electrically conductive member forcausing the head thereof to apply pressure to said disc electrode in adirection pressing the disc electrode against said insulator, and aninsulating composition circumferentially of said electrically conductivemember filling said axial bore of the first electrode and extendingaxially in said tubular body member.

2. A low voltage spark plug according to claim 1, in which saidinsulator comprises a refractory material and is capable of remainingdimensionally stable at elevated temperatures at least-to 1000centigrade.

3. A low voltage spark .plugaccording to claim .1, in which saidinsulator comprises a ceramic having a dielectric constant greater than50. i

4. A low voltage spark plug according to claim 1, in which saidinsulator is enamelled at least on said sparking zone with aspark-supporting enamel.

5. In a low voltage spark plug having a tubular member, a spark-plugcartridge mounted in said body member comprising, a tubular firstelectrode disposed concentric internally ofsaid tubular bodymember atone end thereof and extending axially externally thereof at saidend,said tubular electrode extending axially into said body membersubstantially a greater distance than the axial distance it extendsoutwardly of said bodymember, said tubular electrode having an axialbore with a counterbore in one end of the bore forming a shoulderinternally of said electrode, a washer-like insulator mounted coaxiallywith said electrodein said counterbore and seated on said shoulder, saidinsulator having a peripheral surface makingcontact with an annularinner surface of said first tubular electrode defining said counterboreand having a substantially flat face substantially coplanar with asubstantially fiat end of said electrode corresponding to said electrodeend extending axially out of said body member, a disc electrode mountedcoaxially with said tubular electrode and having a transverse dimensionsmaller than said insulator forming a circumferential gap of uniformdimensions between the disc electrode and the tubular electrode therebyforming a sparking zone of uniform dimensions, andan electricallyconductive, axially displaceable, member disposed extending axially insaid tubular electrode and said body member and having a mushroom headfor holding the discelectrode snug against said coplanar face surface ofthe insulator, means comprising a plurality of dished cooperativelydisposed spring elements disposed externally of the tubular body memberfor adjustably applying an axially directed tension to said electricallyconductive member for causing the head thereof to apply pressure to saiddisc electrode in a direction pressing the disc electrode against saidinsulator, and an insulating composition circumferentially of saidelectrically conductive member filling said axial bore of the firstelectrode and extending axially in said tubular body member.

6. A cartridge for a low voltage spark plug comprising, a tubular firstelectrode, said tubular electrode having an axial bore with acounterbore in one end-of the bore forming a shoulder internally of saidelectrode, a washerlike insulator mounted coaxially with said electrodein said counterbore and seated on said shoulder, said insulator having aperipheral surface making contact with an annular inner surface of saidfirst tubular electrode defining said counterbore and having asubstantially flat face substantially coplanar with a substantially flatend of said electrode corresponding to said electrode end having saidcounterbore, and a disc electrode mounted coaxially with said tubularelectrode and having a transverse dimension smaller than said insulatorforming a circumferential gap of uniform dimensions between the discelectrode and the tubular electrode thereby forming a sparking zone ofuniform dimensions, and an insulating composition filling said axialbore of the first electrode.

7. A cartridge for a low voltage spark plug comprising, a tubular firstelectrode, said tubular electrode having an axial bore with acounterbore in one end of the bore forming a shoulder internally of saidelectrode, a washerlike insulator mounted coaxially with said electrodein said counterbore and seated on said shoulder, said insulator having aperipheral surface making contact with an annular inner surface of saidfirst tubular electrode defining said counterbore and having asubstantially fiat face substantially coplanar with a substantially flatend of said electrode corresponding to said electrode end having saidcounterbore, a disc electrode mounted coaxially with said tubularelectrode and having a transverse dimension smaller than said insulatorforming a circumferential gap of uniform dimensions between the discelectrode and the tubular electrode thereby forming a sparking zone ofuniform dimensions, and an electrically conductive, axiallydisplaceable, member positioned in assembly in said spark-plug extendingaxially in said tubular electrode and having a mushroom head for holdingthe disc electrode snug against said coplanar face surface of theinsulator,

means comprising a plurality of dished spring elements References Citedin the file of this patent UNITED STATES PATENTS 963,334 StonebridgeJuly 5, 1910 1,110,813 Noble Sept. 15, 1914 1,272,954 Horning July 16,1918 1,403,448 Ryder Jan. 10, 1922 2,605,754 Smits Aug. 5, 19522,760,099 Suter Aug. 21, 1956 FOREIGN PATENTS 22,517 Great Britain Sept.28, 1910

